In present day electronic remote control systems which use radio communication between the lead and slave locomotives disposed in a train consist, the software of a brake control computer in the lead locomotive runs certain routines when it receives an emergency brake control signal from a switch operated by an operator's brake handle.
As is well known in the railway braking art, an emergency brake application dumps air from a pneumatic brake pipe of the locomotives and cars connected to the locomotives. The on-board computer will note the resulting rapid reduction of air pressure in such brake pipes, and proceeds to check for possible other causes of such reduction before indicating the handle initiated emergency event.
Other possible causes of a rapid reduction in brake pipe air pressure can be, for example, a broken brake pipe or a loss of electrical power. Loss of electrical power will, for safety reasons, necessarily cause an emergency brake voltage to be generated.